Production of sodium aluminum fluorides



Patented Aug. 23, 1932 i JOHN E. MORE-OW, OF OAKMONT,

VANIA No Drawing.

This invention relates to the production of sodium aluminum fluorides of a high degree of purity from sodium fluoride and aluminum hydrate. The object of the invention is to 5. provide a simple and commercially feasible method of producing an artificial cryolite which has approximately the same chemical composition as the natural mineral cryohte, and which may be used for the same purposes.

Double fluorides of sodium and aluminum occur in nature as the minerals cryolite (N a AlF or 3NaF.Al and chiolite, thefor-I mula of which is reported to be 5NaF.3AlF

For most purposes 'forwhich cryolite is used,

either of these minerals or a mixture of them 'nun1 fluoride in a somewhat different ratio can be employed. The product of my process has a composition approximating Na AlF The product may, however, under some conditions, contain sodium fluoride and alumithan that found in the mineral cryolite and therefore, I preferto describe the product by the general term sodium aluminumfiuoride.

I have discovered that by digesting together suitable amounts of sodium fluoride" and aluminum hydrate there is obtained sodium aluminum fluoride of high purity; I have further discovered that a suitable treatment of the digested solution will enable the recovery of the sodium aluminumfluoride in amounts as high as to of the'theo retical yield. v

' According to my invention sodium fluoride and aluminum hydrate mixed with water are caused to react at temperatures of about 75 C. or above to form a sodium aluminum fluoride and sodium hydroxide, apparently according to the reaction 12NaF 2A1 OH) 3 =2Na AlF oNaOH It is not essential to the success of the reaction that the reagents be pure, in fact, so-' dium aluminum fluoride may be satisfactorilyformed by using impure sodium fluoride and bauxite. However, the. purity of the product is dependent upon the purity ofthe reacting materials and for this reason it is preferable to use a sodium fluoride of high purity and an aluminum hydrate of a purity Application filed December 30, i927. 'serial No. 243,758.

A CORPORATION;

rnonuorrou or-sonru vr ALUMINUM rnuomnns stoi chiometric proportionsnecessary to form, sodium aluminum flllOI'lCl. according to the formula Na Al Anexcess of aluminum 11y.- drate will materlally increase the efliciency of the reaction but, for reasons which will later appear, may not be desirable in amounts over 5%. If stoichiometric proportions of sodium fluoride and aluminum hydrate'are digested together for a short period oftime at theboiling temperature of the solution (about (1), the reaction will proceed to about 25%.co'mpletion. An increase of tern-1 perature to C. tends to further promote the reaction, and at C. it is about 60% complete; at C. about 93%, of the-re agents are converted into sodium fluoride andsodium hydroxide. the-reaction is 95% complete. It is readily apparent-,therefore, that a temperature higher than 175180 C. is not necessary. How ever, higher temperatures can be employed and'are within the scope of my invention, although under ordinary Working conditions, the pressure increase caused by these higher temperatures is not desirable. I a

As above mentioned, the reaction is pro-i moted by the use ,of an excess ofv aluminum hydrate.--However, it has been found that the aluminum hydrate added in excess of the theoretical proportions, will remain in the final product as an impurity, and for thisreason an excess of over 5% isnot ordinarily'desirable. v

In the foregoingdiscussion, the reaction of sodium fluoride with aluminum hydrate has been described as being about 93% complete at 175" C; It was cause of the solubilityof the sodium aluminum fluoride product in the other reaction product, sodium hydroxide, the actual yield. of solid crystalline sodium aluminumfluoridc amounted to only about 40% of the theo-.

retical. a 7

Regardless of this reduced yield of thefinalproduct because 'of the solubility of sodium aluminum fluoride in sodium hydoxide, the

and aluminum hydrate.

aluminum; 'At"'185 0.,

found,however, that be- T eme PENNSYLVANIAASSiGNOR T 0 ALUMINUM coiuPANY:

or AMERICA, or rrrrsnunen, PENNSYLVANIA, or PENNSYL- produced by the iWell reaction, as

above described, is commercially feasible and profitable since the sodium aluminum fluoride-sodiumv hydroxide solution may be filtered from the precipitated product and after suitable treatment returned to the process. However, I have found that such procedure is not necessary since theyi'eld of "the solid product may be considerably increased if the solvent action of the sodium hydroxide is substantially eliminated; I This can be accomplished by adding to the solution a reagent which will neutralize the sodium hydroxide but will not otherwise unfavorably I th product-1 Examples affect the reaction or of such reagents are hydrochloric acid, sulphuric'aeid, sulphur dioxide, sodium bicarbonate, and carbon dioxide; The choice of the reagent may be dependent upon the materials at hand and the'by-product desired.

For the present purpose, the use of carbon partially or completely saturated with car-- bon dioxide. Ordinarily satisfactory results maybe obtained by adding suflicient carbon dioxide to convert the sodium hydroxideto sodium carbonate.

A mixture of sodium fluoride and aluminum hydratewhich has been'digested with water may give a conversion at 175 G., of 93% of the starting material, while the actual yieldof the precipitatedsodium aluminum fluoride will be only about 40%. However, on adding to this solution carbon dioxide or its equivalent, the actual yield of the precipitated sodium aluminum fluoride may bemore than doubled. The sodium carbonate formed maybe used in many for producing the sodium fluoride or for other purposes. H 7

3 At the lower'temperatures,such as, for example 100 (1., the reaction may be caused to proceed more nearly to completion by long periods of digestion, whereasat the preferred temperature the reaction is rapid and the materials need be digested but a short time in order to obtain a practically complete conversion of the sodium fluoride and aluminum hydrate into sodium aluminum fluoride.

As an example of my invention 100 parts (by weight) of sodium fluoride and 32.5 parts of aluminum hydrate were added to 2000 parts of water and digested v 94% complete and 41.4% of the theoretically obtainable amount of sodium aluminum fluoride had been precipitated. The temperature of this solution was lowered to 165 C. and carbon dioxide was added until the solution was saturated. Under these condig V 3. The process'of mak ng num fluoride comprising of the known processes hour at 17 5. C. At the end of this time the reaction was tions the reaction was 94% complete and the yield of precipitated sodium aluminum bride was 93.8% of the theoretical value calculated on the basis of the sodium fluoride.

The solid product had the following analysis E 0 S10. iasso; .na co Sodium-aluminum- A1203 "fluoride By the term ignated as the hydroxides andwhich are more accurately designated as the hydratedoxides ofaluminum, irrespective of the actual degreeof hydration,

lclaimz' i "1.-The'process of makingsodiumaluminum fluoride comprising digesting together sodium fluoride and aluminum hydrate-at;

temperatures above 2. The process of makingsodium alumi num fluoride comprising digesting together sodium fluoride and aluminum hydrate at a temperature ofapproximately 17 5 O sodiumfluoride and aluminum hydrate at temperatures above -75f C." and eliminating the caustic alkaliformed.

aluminum hydrate? I, mean. the'chemical' compounds which are often dessodium 'alumidigest ng together l. The process of *makingsodium N num fluoride comprising digesting'together sodium fluoride and aluminum hydrate ata temperatureof approximately 175 and eliminating the caustic alkali formed. I

- 5. The process of making sodium alumi-' num fluoride comprisingldigesting together sodium fluoride and aluminumhydrate, neu

tralizing the. caustic alkaliyj formedtoincrease the yield of the solid sodium. aluminum fluoride. and separating the solid sodi um'aluminum fluoride from the solution.

6. The process of num' fluoride comprising digesting together sodium fluoride and temperatures j above v7 5. caustic alkali formed j and separating the solid sodium aluminum fluoridefromthe solution.

' 7. The process'of making. sodium"alumi-- num fluoride. comprising. digesting together sodium fluoride and a1iiminum hydr'a'te,"at a temperature o'f a proxim te- ,117? neu-' the caustic alkali. formed and sepafluoride traliz'ing rating the 'soli'dfsodium aluminum from the solution.

8. The process num fluoride comprising sodium fluoride and V verting the caustic alkali formed to a carbonate and separating the sodium aluminum fluoride from thefsolutionlf 9. The process of making sodium "alumi-' num fluoride comprising digesting together of. making sodium alumisodium fluoride and aluminumhydrate at temperatures abovei7 5 (3.," converting the caustic alkali formed to a'fcarbonate and sepmaking sodium alumi-' aluminum hydrate at; 6., neutralizing the digesting together aluminum hydrate, con- 1 temperatures above C., said hydrate be- 7 ing in excess of the stoichiometric propor-' tion required to convert the sodium fluoride into N a A1F 12. The process of making'a sodium aluminum fluoride comprising digesting together sodium fluoride and aluminum hydrate at atemperature of approximately C., said hydrate being in excess of the stoichiometric proportion required to convert the sodium fluoride into N a AlF 13. The process of making a sodium aluminum fluoride comprising digesting together sodium fluoride and aluminum hydrate, said hydrate being in excess of the stoichiometric proportion required to convert the sodium fluoride into N a AlF so as to increase the efliciency of the reaction, neutralizing the caustic alkali formed to increase the yield of the solid sodium aluminum fluoride and separating the solid sodium aluminum fluoride and the excess aluminum hydrate from the solution.

14. The process of making a sodium aluminum fluoride comprising digesting together sodium fluoride and aluminum hydrate at temperatures above 75 (1, said hydrate being in excess of the stoichiometric proportion required to convert the sodium fluoride into Na AlF neutralizing the caustic alkali formed and separating the solid sodium aluminum fluoride and the excess aluminum hydrate from the solution. a

15. The process of making a sodium aluminum fluoride comprising digesting together sodium fluoride and aluminum hydrate at a temperature ofapproximately 175 (3., said hydrate being in excess of the stoichiometric proportion required to convert the sodium fluoride into Na AlF neutralizing the caustic alkali formed and separating the solid sodium aluminum fluoride and the excess aluminum hydrate from the solution.

In testimony whereof I have hereunto aflixed my signature.

JOHN E. MORROW. 

